In short, segregation is what you get when an external force separates out things (or people). A scientist will segregate an animal population for study. The animals in question do not have a choice in the matter and no power to change the situation if they so chose.

Animals or other living organisms "aggregate" or "form communities" of their own volition. External factors such as hostility encountered in other arenas may inform their choices, but they are quite free to deal with such hostility if they so choose. The key being if they so chose. Their neighbors may decide to up and leave ("white flight for example), but that isn't segregation.

We need to tackle the notion that black communities are "segregated" by the fact that they are mostly or all black. The term is rarely used in reference to non-black communities such as Asian or white ethnic neighborhoods.

Playboy:
If Negroes are also granted preferential treatment in housing, as you propose, how would you allay the alarm with which many white homeowners, fearing property devaluation, greet the arrival of Negroes in hitherto all-white neighborhoods?

King:
We must expunge from our society the myths and half-truths that engender such groundless fears as these. In the first place, there is no truth to the myth that Negroes depreciate property. The fact is that most Negroes are kept out of residential neighborhoods so long that when one us is finally sold a home it’s already depreciated. In the second place, we must dispel the negative and harmful atmosphere that has been created by avaricious and unprincipled realtors who engage in “blockbusting.”

If we had in America really serious efforts to break down discrimination in housing, and at the same time a concerted program of Government aid to improve housing for Negros, I think that many white people would be surprised at how many Negroes would choose to live among themselves, exactly as Poles and Jews and other ethnic groups do.[My emphasis]

If Dr. King, who was well informed as to what constituted segregation, could say, without hesitation, that ethnic neighborhoods of any stripe were not "segregated" but rather the results of places where people choose to live, then I think it's high time that black folks stop referring to places with high concentrations of black people as segregated. All it serves is to stigmatize the neighborhoods and their residents. It also serves to devalue the communities and, in my opinion, is a part of the mentality that informs much of the violence (gun and other) that is displayed by those living in such places.